An encoder of a sensor usually utilizes an optical, magnetic or mechanical contact way to sense the location, and outputs an electrical signal converted from the location for being a feedback signal to control the location. The encoders can be divided into rotary encoders and linear encoders according to the motion mode. A rotary encoder is usually installed in the rotating objects, such as a motor shaft. The rotary encoder may convert the rotating location or the rotating amount into the analog signal, such as analog quadrature signal, or the digital signal, such as 32-bit parallel signal or digital orthogonal signals.
An encoder may be absolute-typed or incremental-typed. The signals output from absolute-typed encoder partition the position information into a plurality of regions, and each region has its unique number. Therefore, even when lacking the previous location information, the unique number output from the encoder still can provide the definite location information. The signal of the incremental-typed encoder is periodic, and the signal itself cannot provide definite location information. Only continuously counting the signals could obtain the definite location information when a certain location is taken as a reference.
Take the high-level machine tool (machining accuracy is about 1 micron) as an example, the server system of the machine tool usually uses the absolute-typed optical encoder having 24-bit per revolution. With the introduction of energy saving and lightweight design, an optical encoder of high positioning resolution may face the problems of the processing size and the assembly accuracy. Also due to the reduction of scale, the optical encoder encounters the environmental oil pollution and the vibration problem, thereby resulting in signal distortion or even failure. In addition, conventional optical encoders are designed by using geometric optics. It is easy to cause the sensing interference of the adjacent beams.